Control of buoyancy in presently available divers jackets is achieved by utilizing compressed breathing gas contained in a tank carried on the best or jacket. Usually, air cells or bladders are incorporated in the jacket and may be inflated relatively easily by opening a valve to permit the inflow of breathing gas. On the other hand, deflation is awkward for the diver, for he must assume an upright position and hold an outlet hose attached to the bladder above his head with the deflation valve open to allow water pressure to force gas out of the bladder into the surrounding ocean. It would be desirable, of course, for the diver to be able to inflate or deflate the jacket no matter what his position, preferably by the manipulation of simple control valves. The diver's control of his buoyancy would thus be greatly simplified. Also, the more compact device made possible would decrease bulk and lessen water drag encountered by the diver while swimming. Finally, a precise control or trimming of buoyancy would be most useful to the diver.